1. Field of the Invention
The present invention relates to a gas sampling bag and, more particularly, to a gas sampling bag that is connected to a constant volume sampling passage, contains a pipe, on which a plurality of gas inlet/outlet holes are formed, in a bag main body, and allows gas to flow into/out of the bag main body through the gas inlet/outlet holes.
2. Background Art
One of the sampling methods of emission gas exhausted from an automobile engine or the like is, for example, the constant volume sampling (CVS) method. In this CVS method, the emission gas having transiently changing flow rate is diluted with the air, and the flow rate of the diluted gas is defined as known flow rate, and the weight of components is calculated by using the diluted gas component concentration and the known flow rate.
In one of the measuring techniques of gas concentration of the CVS method, the sampled diluted gas is put in a gas sampling bag, and the gas in this gas sampling bag is supplied into a gas analyzer.
FIG. 5 schematically shows a conventional example of this gas sampling bag. In FIG. 5, reference numeral 51 denotes a gas sampling bag, and reference numeral 52 denotes a bag main body stretchably formed by gluing, for example, fluoroplastic sheets. Reference numeral 53 is a pipe made of, for example, fluoroplastic material of a circular cross-section provided inside the bag main body 52, and it is formed like a shape of 8 in plan view. In the middle of the pipe 53, a gas junction 54 is formed as a junction to an external gas passage, and a plurality of gas inlet/outlet holes 55 of proper small diameter are formed at uniform intervals on the periphery of the overall length of the pipe 53.
In the gas sampling bag 51 having such a configuration, the gas junction 54 is connected to the constant volume sampling passage through a valve and, by opening the valve, the gas from the constant volume sampling passage is introduced into the pipe 53 through the gas junction 54 and flows into the bag main body 52 through the plurality of gas inlet/outlet holes 55. In the bag main body 52, the gas is mixed securely, and a gas of uniform concentration is prepared. The gas sampling bag 51 is connected to a gas supply path to a gas analyzer through a valve and, by opening the valve, the gas in the bag main body 52 flows into the gas junction 54 through the plurality of gas inlet/outlet holes 55 and pipe 53 and flows out in the gas supply direction.
In the conventional gas sampling bag 51, however, in order to decrease the pressure loss of the gas when passing the gas inlet/outlet holes 55 as much as possible, when the inner diameter of the pipe 53 is, for example, 6 mm, this pipe 53 has 52 gas inlet/outlet holes 55 each having an opening diameter of, for example, 3 mm. In the gas sampling bag 51 formed in this manner, if the concentration changes significantly in the constant volume sampling passage, gas mixing in the bag main body 52 is not always sufficient, and the gas concentration in the bag main body 52 is not always uniform.
To avoid uneven gas concentration in the bag main body 52 of the gas sampling bag 51, the gas filling rate in the bag main body 52 may be raised, the gas injection time in the bag main body 52 may be extended, or the gas flowing rate into the bag main body 52 may be increased. However, in the gas sampling bag 51 connected to the constant volume sampling passage, the overall capacity of the bag main body 52 is limited, and cannot be increased simply in relation to the test mode duration and injection flow rate.
Under such restrictions, the present inventors investigated and discovered as follows: in the conventional gas sampling bag 51, it was attempted to minimize pressure loss of gas when passing the gas inlet/outlet holes, and all gas flowing into the pipe 53 through the gas junction 54 does not flow into the bag main body 52 through all of gas inlet/outlet holes 55, but flows into the bag main body 52 through a limited number of gas inlet/outlet holes 55 in the vicinity of the gas junction 54; therefore, there is a high possibility in that the gas was not mixed sufficiently.